1. Technical Field
The present disclosure is directed to a method and system for determining and dispensing resin accurately for a compression molding process flow.
2. Description of the Related Art
A variety of techniques are used to form packages for semiconductor dice (or dies). Manufacturers have parameters or specifications for their packages in order to have consistency in size, shape, and operation. Some techniques are more accurate than others in providing packages that meet the parameters set by the manufacturer.
For example, one technique is transfer molding in which a carrier, on which are a plurality of individual dice, is placed into a mold tool. The mold tool includes a top portion and a bottom portion that are configured to seal the carrier with the dice within a mold cavity. Pellets of mold compound are loaded into a mold pot bushing before the top and bottom portion are brought into contact. The pellets are moved by a transfer plunger from the mold pot bushing into the mold cavities.
Regardless of the number of dice on the carrier, the mold tool compensates for cull, which is excess mold compound from the mold cavity. For example, if a particular batch of dice are thicker, then the resulting cull from the transfer process will be thicker. At the other end of the spectrum, such as when fewer dice are placed on the carrier than the carrier can hold, the same amount of mold compound will result in negative cull. Negative cull exists when there is insufficient mold compound in the mold cavity due to dice missing from the carrier or other defects. This can result in cosmetic surface defects to the packages formed by the transfer molding.
Another technique used to form packages for semiconductor die is compression molding. Compression molding machines scan the carriers to determine a number of dice present on the carrier, the sizes of the dice on the carrier, and the thicknesses of the dice. This die scanning is performed by laser or camera based scanning devices within the compression molding devices. The data is processed within the molding devices to determine an amount of resin to dispense into a mold cavity to achieve a specific thickness of the packages.
If the data provided by the scanners is inaccurate, too much or too little resin is dispensed into the mold cavity. This can cause irregularities in the packages. The resin calculation utilizes the number of dice, the carrier dimensions, and the dice thicknesses, to determine the amount of resin. If any of these parameters are inaccurate, the amount of resin will be negatively impacted.
The scanning techniques, either laser or visual, are often imprecise. For example, some scanning techniques use a vacuum to hold the carrier flat during the scanning. However, in some instances, there is vacuum leakage, which causes the carrier to warp and thus results in an inaccurate scan. Warpage of the carrier can result in failure to detect different thicknesses between the dice and failure to detect the presence of thin dice.
The scanners have difficulty determining differences in thickness between dice on the carrier, small dice may not be detected during scanning, or the scanner may detect a die pad as a die even if a die is not present. If the die is thinner than detected, the amount of mold compound provided will be less than what the machine actually needs to form the package within a set of parameters. Alternatively, if the die is thicker than detected, the final package may be larger than the manufacturer's parameters.
In some circumstances, the inconsistencies in the final packages may cause the manufacturer to scrap or otherwise throw out the irregular packages. These inaccuracies in scanning reduce yield and are costly for the manufacturer.